1. Field of the Invention
The present invention relates to a process for wet chemical metallization of a substrate by precipitating a metal layer onto a cleansed, and optionally roughened, substrate.
2. Background of the Art
Various substrate materials, metallic and non-metallic, are frequently covered with metal layers so as to produce certain functional or decorative characteristics. These metal layers generally must be able to withstand various stresses encountered during subsequent processing or in use. In particular, a permanent and sufficiently great adhesion between the substrate material and the metal layer is a basic prerequisite for practical use. Adhesion must be sufficient also under high mechanical loads from thermal stresses due to high temperatures or due to fluctuations in temperature.
Generally the adhesion of metal layers to non-metallic substrates is not great enough to prevent bubble formation in the metal layer under thermal stresses encountered, for example, during soft soldering. For this reason, only such processes as, for example, vacuum vapor deposition, cathode sputtering or the chemical vapor deposition (CVD) technique, which require expensive apparatus and are generally not economical, are available for the production of metallizations on non-conductors which are to be subjected to thermal stresses.
It is an object of the present invention to provide a process of the above-identified species which permits, in particular, the economical, wet chemical metallization of a substrate, especially an electrically insulating substrate, so that the best possible adhesion of the metal layer to the substrate is realized and the metallization is thermally stressable, particularly when subjected to a soft soldering process as is customarily used in electrical applications.